The Joomla has a nifty, often used feature, along other information can show the content item's/articles author name just below the title. It's useful especially when the site is maintained by a number of editors and/or contributors. But sometimes - especially when the site is just launched - all authors are the same. The explanation is simple, Joomla assigns by default as author of the article the user who created/entered it in Joomla's content manager. And this, at beginning, is generally the Administrator user, or the editor in charge to launch the site. What you can do?

First impulse of almost every Joomla Admin wannabe is to turn off the switch and don't show at all who's the creator.

Simple brute-force approach, don't you?

But what if you still want the author names? Don't despair, there are at least 2 solutions to fix this on per article/content item basis:

1. The author has an existing username/login on the site, then you can simply change the creator's name from the Change Creator: dropdown in the Content edit window, right pane, Publishing tab (might be a bit different in different Joomla versions, but the functionality is the same in all existing Joomla versions.)
2. The author does not have username/login on the site, then in same menu use the Author Alias: field to indicate the real author.

From the frontend, both solutions have the same effect: you will see the desired name listed as Author for that particular article.